Conventional horizontal skylights suffer from poor sunlight collection when the sun is low in the sky, i.e., when the sun's elevation angle is small. This poor low-sun-elevation angle performance leads to poor lighting in the wintertime in most moderate latitudes, and to poor lighting early and late in the day in all locations. Previous attempts to solve this problem have sometimes used expensive tracking reflectors above the skylight penetration into the building, or sometimes used fixed reflectors or prismatic lenses above the skylight penetration with less than adequate performance.
Conventional horizontal skylights also suffer from excess sunlight collection when the sun is high in the sky, i.e., when the sun's elevation angle is large. This excess sunlight collection during summer months near solar noon increases solar heat gain with corresponding increases in air conditioning loads and costs. Previous attempts to solve this problem have sometimes used expensive blinds and baffles to block some of the excess sunlight collection with less than satisfactory performance, reliability, and cost.
The present subject matter uses a relatively tall diffusely transmitting dome to collect low sun elevation light, with an opaque shade near the top of the dome to block high sun elevation light, thereby solving both problems by both increasing inadequate sunlight collection during low sun elevation periods and also by decreasing excess sunlight collection during high sun elevation periods. The present subject matter solves both problems in a totally passive manner, requiring no moving parts and no seasonal change in configuration of the skylight. Therefore, the present subject matter represents a simple, reliable, cost-effective solution to two major problems for horizontal skylights.
This subject matter includes at least one skylight dome with relatively tall partially vertical sides comprising partially transparent material which diffuses the transmitted light, and at least one mostly opaque sun shade near the top of the relatively tall partially vertical sides. The partially vertical sides are able to better intercept sunlight from low sun elevation angles, in contrast to conventional horizontal skylights which are less well able to intercept such low-sun-elevation-angle light. The mostly opaque sun shade is able to block sunlight from high sun elevation angles to prevent such sunlight from entering the building below the dome. By enhancing the collection of low-sun-elevation-angle light, the subject matter improves the daylighting performance of the skylight early and late in the day year-around, and all day in the winter months of the year. By reducing the collection of high-sun-elevation-angle light, the subject matter reduces the solar heat gain near solar noon in the summer months, thereby reducing air conditioning loads and related costs for equipment and operating energy. The simple passive configuration of the subject matter, with no moving parts and no operational complexity, ensures high reliability and low maintenance.
These and many other advantages of the present subject matter will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.